System for optically detecting an electrical arc in a power supply

ABSTRACT

A system for optically detecting an electrical arc in a power supply. The system includes a light pipe, a photodetector optically coupled to the light pipe, and a signal processor connected to the photodetector.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of U.S. Provisional PatentApplication No. 60/801,929, filed on May 19, 2006.

BACKGROUND

This application discloses an invention that is related, generally andin various embodiments, to a system for optically detecting anelectrical arc in a power supply. The system and may be utilized with apower supply having a plurality of power cells. Various embodiments of apower supply having a plurality of power cells are described, forexample, in U.S. Pat. No. 5,625,545 to Hammond (“the '545 patent”).

Systems for optically detecting an electrical arc are known in the art.In general, when an electrical arc occurs, the light resulting from thearc is optically detected, and the detection may be utilized tointerrupt the power that is supplying the electrical arc. However, knownsystems for optically detecting electrical arcs are not necessarilysuitable for many applications.

Known systems for optically detecting electrical arcs are generallysusceptible to a single point of failure, and thus are not particularlywell-suited for applications which require a particular level ofredundancy. Also, in various devices, electrical arcs can occur in avariety of locations. For such a device, electrical arcs can occur inlocations which are not quickly detected by known optical arc detectionsystems. Consequently, the detection of such arcs is often delayed,thereby allowing the arcs to cause significant damage to the deviceprior to their detection. In many instances, the damage is significantenough to render the device inoperable.

SUMMARY

In one general respect, this application discloses a system foroptically detecting an electrical arc in a power supply. According tovarious embodiments, the system includes a light pipe, a photodetectoroptically coupled to the light pipe, and a signal processor connected tothe photodetector.

In another general respect, this application discloses a power supply.According to various embodiments, the power supply includes a pluralityof power cells. At least one of the power cells includes at least aportion of a light pipe, a photodetector optically coupled to the lightpipe, and a signal processor connected to the photodetector.

Aspects of the disclosed invention may be implemented by a computersystem and/or by a computer program stored on a computer-readablemedium. The computer-readable medium may comprise a disk, a device,and/or a propagated signal.

DESCRIPTION OF DRAWINGS

Various embodiments of the invention are described herein by way ofexample in conjunction with the following FIGS.

FIG. 1 illustrates various embodiments of a system for opticallydetecting an electrical arc;

FIG. 2 illustrates various embodiments of a light pipe of the system ofFIG. 1;

FIG. 3 illustrates various embodiments of a signal processing circuit ofthe system of FIG. 1;

FIG. 4 illustrates various embodiments of a digital signal processor ofthe system of FIG. 1;

FIG. 5 illustrates various embodiments of a digital signal processor ofthe system of FIG. 1;

FIG. 6 illustrates various embodiments of a power supply which includesthe

system of FIG. 1;

FIG. 7 illustrates various embodiments of a power cell of the powersupply of FIG. 6;

FIG. 8 illustrates various embodiments of a power cell of the powersupply of FIG. 6;

FIG. 9 illustrates various embodiments of a power supply which includesthe system of FIG. 1; and

FIG. 10 illustrates various embodiments of a method for opticallydetecting an electrical arc.

DETAILED DESCRIPTION

It is to be understood that at least some of the figures anddescriptions of the invention have been simplified to focus on elementsthat are relevant for a clear understanding of the invention, whileeliminating, for purposes of clarity, other elements that those ofordinary skill in the art will appreciate may also comprise a portion ofthe invention. However, because such elements are well known in the art,and because they do not necessarily facilitate a better understanding ofthe invention, a description of such elements is not provided herein.

FIG. 1 illustrates various embodiments of a system 10 for opticallydetecting an electrical arc. The system 10 includes a light pipe 12, aphotodetector 14 optically coupled with the light pipe 12, and a signalprocessor 16 electrically connected to the photodetector 14. The system10 may be utilized to optically detect an electrical arc in a variety ofapplications. For example, the system 10 may be utilized to opticallydetect an electrical arc in a power supply having a plurality of powercells. Various embodiments of a power supply having a plurality of powercells are described, for example, in U.S. Pat. No. 5,625,545 to Hammond(“the '545 patent”), which is hereby incorporated by reference in itsentirety. For ease of explanation purposes, the system 10 will bedescribed in the context of optically detecting an electrical arc in apower supply which is similar to the power supply described in the '545patent. However, the system 10 may also be utilized to optically detectan electrical arc in applications other than a power supply.

Various embodiments of the light pipe 12 are illustrated in FIG. 2. Thelight pipe 12 includes a first end 18 and a second end 20, and may be ofany suitable length. According to various embodiments, the light pipe 12is configured to capture light present at its first end 18 and transmitthe captured light along the length of the light pipe 12 to its secondend 20. According to various embodiments, the light pipe 12 is alsoconfigured to capture light present along its length and transmit thecaptured light along the length of the tight pipe 12 to its second end20. Thus, in operation, when light associated with an electrical arc isproximate any portion of the light pipe 12, the light is captured andtransmitted along the length of the light pipe 12 to its second end 20.

Returning to FIG. 1, as indicated hereinabove, the light pipe 12 isoptically coupled with the photodetector 14. Such optical coupling maybe realized by positioning an end of the light pipe 12 (e.g., the secondend 20 of the light pipe 12) proximate the photodetector 14. Forapplications where the second end 20 of the light pipe 12 is positionedproximate the photodetector 14 (e.g., see Fig. X), light captured at thefirst end 18 of the light pipe 12 and/or along its length is transmittedto the photodetector 14 via the second end 20 of the light pipe 12.

The photodetector 14 may be any suitable type of photodetector. Forexample, according to various embodiments, the photodetector 14 is aphotodiode having an anode and a cathode as is known in the art. Forembodiments where the photodetector 14 is a photodiode, the photodiodemay be a P-N photodiode, a P-I-N photodiode, etc., and may have aspectral range of approximately 350 to 1100 nanometers. According toother embodiments, the photodetector 14 is a phototransistor.

For some embodiments where the photodetector 14 is a photodiode, thephotodiode is reverse-biased, operates in the photoconductive mode, andmay generate a measurable level of dark current. For such embodiments,the cathode of the photodetector 14 is connected to a power source 22and the anode of the photodetector 14 is connected to the signalprocessor 16. The power source 22 may form a portion of the system 10 ormay be external to the system 10. For other embodiments where thephotodetector 14 is a photodiode, the photodiode is zero-biased andoperates in the photovoltaic mode. For such embodiments, thephotodetector 14 is not connected to the power source 22 and the cathodeof the photodetector 14 is connected to the signal processor 16.

In operation, when the photodetector 14 optically detects lightassociated with an electrical arc (e.g., when light associated with anelectrical arc is captured by the light pipe 12 and is transmitted tothe photodetector 14), the photodetector 14 generates a current which isrepresentative of the intensity of the detected light. The generatedcurrent may include a photocurrent component and a dark currentcomponent. The photocurrent component may be considered an arc componentof the generated current, and the dark current component may beconsidered a non-arc component of the generated current.

As indicated hereinabove, the signal processor 16 is electricallyconnected to the photodetector 14. The signal processor 16 may beimplemented in any suitable manner. For example, according to variousembodiments, the signal processor 16 is implemented as a signalprocessing circuit. Various embodiments of such a signal processingcircuit are illustrated in FIG. 3. The signal processing circuit 30 ofFIG. 3 includes an RC filter circuit 32 and a trip circuit 34 which areeach electrically connected to the photodetector 14. The RC filtercircuit 32 operates to remove unwanted information (e.g., informationrepresentative of the dark current component) from the signal generatedby the photodetector 14. The trip circuit 34 operates to output a signalwhen the voltage applied to the trip circuit 34 reaches or exceeds apredetermined threshold.

According to other embodiments, the signal processor 16 is implementedas a digital signal processor. Various embodiments of such a digitalsignal processor are illustrated in FIGS. 4 and 5. The digital signalprocessor 40 of FIG. 4 includes a filter module 42 and a comparatormodule 44 in communication with the filter module 42. The filter module42 is configured to generate a signal representative of the photocurrentcomponent of the signal generated by the photodetector 14. Thecomparator module 44 is configured to compare a value of the filteredsignal to a threshold value, and generate an output based on which ofthe two values (i.e., the value of the filtered signal or the thresholdvalue) is larger. The modules 42, 44 may be implemented in hardware, infirmware, in software, or in any combination thereof. According tovarious embodiments, the functionality of the modules 42, 44 may becombined into a single module or distributed over more than two modules.

The digital signal processor 50 of FIG. 5 includes a filter module 52,an amplitude module 54 and a frequency module 56. The filter module 52is configured to generate a signal representative of the photocurrentcomponent of the signal generated by the photodetector 14. The amplitudemodule 54 is in communication with the filter module 52, and isconfigured to analyze the amplitude of the filtered signal. Thefrequency module 56 is also in communication with the filter module 52,and is configured to analyze the frequency of the filtered signal.Collectively, the amplitude module 54 and the frequency module 56operate to spectrally break down the filtered signal. By analyzing boththe amplitude and frequency of the filtered signal, the digital signalprocessor 50 may determine the specific type of arcing which hasoccurred, and generate an output based on the analysis. The modules 52,54, 56 may be implemented in hardware, in firmware, in software, or inany combination thereof. According to various embodiments, thefunctionality of the modules 52, 54, 56 may be combined into a singlemodule or distributed over more than three modules.

In some implementations of the system 10, the filtering function may beapplied external to the digital signal processors of FIGS. 4 and 5(e.g., by an RC filter). For embodiments where the signal generated bythe photodetector 14 is an analog signal, the system 10 may also includean analog-to-digital converter (not shown) electrically connected to thephotodetector 14 and the digital signal processor to convert the analogsignal generated by the photodetector 14 to a digital signal which issuitable for the digital signal processor,

FIG. 6 illustrates various embodiments of a power supply 60. The powersupply 60 may be similar to the power supply described in the '545patent. The power supply 60 includes a multi-winding device 62 such as atransformer or a transformer-like device, a plurality of power cells 64connected to the multi-winding device 62, and a main control 66connected to each of the power cells 64. The power supply 60 may alsoinclude a main contactor 68 which is connected to the power input of thepower supply 60, to the multi-winding device 62, and to the main control66. The main contactor 76 may be a three-phase contactor connected tothree power lines of a three-phase distribution system, and may compriseany number of auxiliary contacts as is known in the art. According tovarious embodiments, the main contactor 68 may be a vacuum contactor,and may be rated for the full current and voltage of a load (e.g., amotor) coupled to the power supply 60.

The power supply 60 may be utilized to deliver a three-phase AC voltageto a motor, and the voltage can vary from application to application.For example, according to various embodiments, the power supply 60 maybe utilized to deliver 4160 volts (vac) to the motor, 6600 volts (vac)to the motor, 10,000 volts (vac) to the motor, or other AC voltagelevels.

Each power cell 64 is a device which includes an AC-DC rectifier, asmoothing filter, an output DC-to-AC converter, and a local control 70.According to various embodiments, the local control 70 may include forexample, the signal processor 16 of FIG. 1. The local control 70 of eachpower cell 64 is in communication with the main control 66. Each powercell 64 may be constructed to low-voltage standards, accepts three-phaseAC input powder, and output a single-phase AC voltage. At least one ofthe power cells 64 of the power supply 60 also includes the system 10 ofFIG. 1. For purposes of clarity, portions of FIG. 6 are shown in aconventional one-line format, and only some of the components of thepower cells 64 (e.g., the local control 70) are shown in FIG. 6. Forexample, although at least one power cell 64 includes a photodetector 14and a signal processor 16 as described with respect to the system 10 ofFIG. 1, such components are not shown in FIG. 6. Although the powersupply 60 is shown as having nine power cells 64 in FIG. 6, one skilledin the art will appreciate that the power supply 60 may include anynumber of power cells 64, and the number of power cells 64 included inthe power supply 60 can vary from application to application.

FIG. 7 illustrates various embodiments of one of the power cells 64. Asshown in FIG. 7, the first end 18 of the light pipe 12 is positionedexternal to the power cell 64 and the second end 20 of the light pipe 12is positioned proximate the photodetector 14. As electrical arcs mayoccur in areas external to the power cell 64, the portion of the lightpipe 12 external to the power cell 64 may capture light resulting fromsuch an arc and transmit the light along its length to the photodetector14. According to other embodiments, the first end 18 of the light pipe12 is positioned internal to the power cell 64 and the second end 20 ofthe light pipe 12 is positioned proximate the photodetector 14.

FIG. 8 illustrates various embodiments of one of the power cells 64. Asshown in FIG. 8, the power cell 64 includes power electronics 72 and aplurality of capacitors 74. The photodetector 14 is positioned to definea field of view 76 within the power cell 64. When positioned in such amanner, the photodetector 14 is able to optically detect an electricalarc occurring at any point within the field of view 76. As electricalarcs are most likely to occur in the area where the power electronics 72are positioned, and the field of view 76 includes the area where thepower electronics 72 are positioned, the photodetector 14 is able tooptically detect electrical arcs originating from the power electronics72, either directly or indirectly via the light pipe 12. For purposes ofclarity, the light pipe 12 is not shown in FIG. 8.

FIG. 9 illustrates various embodiments of a power supply 80. The powersupply 80 may be similar to the power supply 60 of FIG. 6, but isdifferent in that the power supply 80 may include a bypass control 82,at least one contactor 84 connected to the bypass control. 82, and atleast one bypass switch 86 connected to the bypass control 82. The atleast one contactor 84 and the at least one bypass switch 86 are alsoconnected to an individual power cell 64. According to variousembodiments, the power cell 80 includes a plurality of contactors 84,wherein each respective contactor 84 is connected to a different powercell 64.

The bypass control 82 and the main control 66 are configured tocommunicate with one another via communication link 88. Communicationlink 88 may be embodied as, for example, a wired connection or a fiberoptic link. The communications between the main control 66 and thebypass control 82 may be in any suitable form. The bypass control 82 maybe implemented in any suitable manner. For example, according to variousembodiments, the bypass control 82 is implemented as a programmablelogic device. The bypass control 82 is operative to receive acommunication from the main control 66, and to transmit a signal to atleast one of the contactor 84 and the bypass switch 86 in responsethereto. The signal transmitted to the contactor 84 and/or the bypassswitch 86 may be a low-voltage signal (e.g., 36 volts). According tovarious embodiments, the power supply 80 may include a plurality ofbypass controls 82, wherein each bypass control 82 is in communicationwith the main control 66 and is connected to a contactor 84 and/or abypass switch 86 associated with a particular power cell 64.

According to various embodiments, the contactor 84 includes contacts 90connected to secondary windings of the multi-winding device 62, and asolenoid 92 connected to the bypass control 82. The number of contacts90 may vary based on the power supply configuration. The solenoid 92 isoperative to open and close each of the contacts 90 responsive to asignal received from the bypass control 82. The contactor 84 may beimplemented as a three-phase contactor, and may include any number ofauxiliary contacts as is known in the art. According to variousembodiments, the contactor 84 may be a vacuum contactor, and may berated for the full current and voltage of the power cell 64 to which itis connected.

The bypass switch 86 may be implemented in any suitable manner. Forexample, according to various embodiments, the bypass switch 86 mayinclude a switch 94 connected to the output of the power cell 64, and aswitch 96 connected to the output of another power cell which isconnected in series with the power cell 64. According to variousembodiments, the switches 94, 96 may be interlocked, and the bypassswitch 86 may further include device (e.g., a solenoid) operative toopen the switch 94 and close the switch 96 responsive to a signalreceived from the bypass control 82.

FIG. 10 illustrates various embodiments of a method 100 for opticallydetecting an electrical arc. The method 100 may be implemented by thesystem 10 of FIG. 1, and may be utilized to optically detect anelectrical arc in a variety of applications. For example, the method 100may be utilized to optically detect an electrical arc within or externalto a power cell in a power supply. For ease of explanation purposes, themethod 100 will be described in the context of optically detecting anelectrical arc in the power supply 80 of FIG. 9. However, the method 100may also be utilized to optically detect an electrical arc in otherpower supplies (e.g., power supply 60 of FIG. 6) and in applicationsother than a power supply.

The process starts at block 102, where the photodetector 14 opticallydetects light resulting at least in part from an electrical arc whichoccurs in the power supply 80. The electrical arc may occur internal toor external to a power cell 64 of the power supply 80. Thus, the lightmay be optically detected by the photodetector 14 directly or via thelight pipe 12.

From block 102, the process advances to block 104, where thephotodetector 14 generates a current (i.e., a signal) which isindicative of the intensity of the detected light. The generated currentincludes a photocurrent component and a dark current, component. Thephotocurrent component is associated with the light resulting from theelectrical arc and the dark current component is associated withsomething other than the electrical arc (e.g., ambient light).

From block 104, the process advances to block 106, where the signalprocessor 16 receives at least a portion of the signal generated by thephotodetector 14, processes the received, signal, and generates anoutput. As described hereinabove, the signal processor 16 may form aportion of the local control 70. The processing of the signal at block106 may include, for example, filtering the dark current component ofthe signal generated by the photodetector 14, comparing the signal orthe filtered signal to a threshold value, and analyzing the amplitudeand/or frequency of the signal or the filtered signal. The outputgenerated by the signal processor 16 may indicate that no arc has beendetected, that an arc has been detected, or that a specific type of archas been detected.

From block 106, the process advances to block 108, where the localcontrol 70 communicates a message to the main control 66. The messagemay indicate, for example, that no arc has been detected, that an archas been detected, or that a specific type of arc has been detected.

From block 108, the process advances to block 110, where the maincontrol 66 receives the message and determines an appropriate course ofaction. The appropriate course of action may be, for example, tointerrupt power to all the power cells, to interrupt power to aparticular power cell (e.g., the power cell which includes photodetectorwhich detected the presence of the arc), or to take no action.

If the determination made at block 110 is to interrupt power to all ofthe power cells, the process advances from block 110 to block 112. Atblock 112, the main control 66 outputs a signal which causes thecontactor 68 to interrupt power to the input to the power supply 80,thereby interrupting power to each of the power cells 64.

If the determination made at block 110 is to interrupt power to aparticular power cell (e.g., the power cell which includes thephotodetector which detected the presence of the arc), the processadvances from block 110 to block 114. At block 114, the bypass control82 receives the interrupt message, processes the interrupt message, andsends an interrupt signal to the contactor 84 associated with theparticular power cell 64. The interrupt signal causes power to beinterrupted to the particular power cell 64. Additionally, the bypasscontrol 82 may also send a bypass signal to the bypass switch 86associated with the particular power cell 64. The bypass signal causesthe switch 94 to open and the switch 96 to close, thereby preventing theparticular power cell 64 from contributing to the output voltage of thepower supply 80 while allowing the power supply 80 to remainoperational.

If the determination made at block 110 is to take no further action, theprocess advances from block 110 to block 116. At block 116, the method100 then waits for the next electrical arc to occur. The process flowdescribed hereinabove may be repeated any number of times while thepower supply 80 is operational.

While several embodiments of the invention have been described herein byway of example, those skilled in the art will appreciate that variousmodifications, alterations, and adaptions to the described embodimentsmay be realized without departing from the spirit and scope of theinvention defined by the appended claims.

1. A system for optically detecting an electrical arc in a power supply,the system comprising: a plurality of power cells; for each of thecells, a light pipe, wherein a first portion of the light pipe ispositioned external to the cell to capture light that may occur from anexternal arc, and a second portion of the light pipe is positionedinside the same power cell to capture light that may occur from an arcwithin the power cell; a plurality of photodetectors, wherein at leastone a photodetector is optically coupled to each light pipe; and atleast one signal processor electrically connected to each photodetector.2. The system of claim 1, wherein each light pipe delivers light to thephotodetector that is optically coupled to the light pipe.
 3. The systemof claim 1, wherein the at least one photodetector that is opticallyconnected to each light pipe is a phototransistor.
 4. The system ofclaim 1, wherein the at least one photodetector that is opticallyconnected to each light pipe is a photodiode.
 5. The system of claim 1,wherein the at least one photodetector that is optically connected toeach light pipe is positioned proximate an end of its correspondinglight pipe.
 6. The system of claim 1, wherein the signal processorcomprises a signal processing circuit which comprises at least one ofthe following: a filter circuit; and a trip circuit.
 7. The system ofclaim 1, wherein the signal processor comprises a digital signalprocessor.
 8. The system of claim 7, wherein the digital signalprocessor comprises a filtering module configured to filter a signalgenerated by at least one photodetector.
 9. The system of claim 7,wherein the digital signal processor comprises a comparator moduleconfigured to compare a value of at least a portion of a signalgenerated by the at least one photodetector with a threshold value. 10.The system of claim 7, wherein the digital signal processor comprises atleast one of the following: an amplitude module configured to analyze atleast a portion of a signal generated by the at least one photodetector;and a frequency module configured to analyze the at least a portion ofthe signal generated by the at least one photodetector.
 11. The systemof claim 1, further comprising a bypass control connected to a maincontrol of the power supply.
 12. The system of claim 11, furthercomprising: a contactor connected to the bypass control and the at leastone of the power cell; and a bypass switch connected to the bypasscontrol, wherein the bypass control activates the bypass switch in theevent an electrical arc is detected in at least one of the power cellsconnected to the bypass switch, thereby bypassing the power cell orcells where the electrical arc was detected.
 13. The system of claim 12,wherein the bypass switch comprises: a first switch connected to anoutput terminal of the power cell that is connected to the contactor;and a second switch connected to an output terminal of another powercell of the power supply.
 14. The system of claim 1, further comprisinga main contactor connected to a main control of the power supply.
 15. Apower supply, comprising: a plurality of power cells, wherein at leastone of the power cells comprises: at least a portion of a light pipe; aphotodetector optically coupled to the light pipe to capture any lightin the power cell resulting from an electrical arc ; and a signalprocessor connected to the photodetector.
 16. The power supply of claim15, further comprising a main control in communication with the powercells.
 17. The power supply of claim 16, further comprising a bypasscontrol in communication with the main control.
 18. The power supply ofclaim 17, further comprising at least one of the following: a contactorconnected to the bypass control and one of the power cells; and a bypassswitch connected to the bypass control.
 19. The system of claim 18,wherein the bypass switch comprises: a first switch connected to anoutput terminal of the one of the power cells; and a second switchconnected to an output terminal of another one of the power cells of thepower supply.